Regeneration of spent caustic



.July 19, 1960 c. o. PETTY 2,945,889

REGENERATION OF SPENT CAUSTIC Original Filed Dec. 21, 1955 CRACKEDGASOLINE I0 I u '6 l4- as RACTOR- CRACKED 2 0 3o 0 BATCH EXT 0 0GASOLINE .124 3 0 r v 36 RAW avnaocmaou STREAM D DILUTED TION 0 BATCHEXTRACTOR. 0

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T. PURE HYOR-OCARBON I5 I soLvEN-r lea REGENEQWED mm I14 INVENTORCHARLES o. PETTY ew REACTION EM BY U ATTORNEY United States Pate-fiREGENERATION OF SPENT CAUSTIC Charles (lrPetty, Tyler, Tern, assignor toLa Gloria Oil and Gas Company, Tyler, Tex., a corporation of DelawareOriginal application Dec. 21, 1955, Ser. No. 565,289,

now Patent No. 2,862,804, dated Dec. 2, 1958. Divided and thisapplication Oct. 29, 1957, Ser. No. 693,505 1 4 Claims. (Cl. 260-609)This invention broadly relates to regeneration of spent caustic solutioncontaining both alkali phenolate and thiol to remove thiol.

According to this invention I have discovered that phenol in substantialconcentration, substantially greater than the thiol content and usuallyexceeding about '5 volume percent, preferably inaqueous alkali solution,catalyzes the reaction between epoxide and organo thiol (mercaptan).Notwithstanding epoxides are known to react readily with phenols, I'havefound that the epoxide will-selectively and preferentially react withorgano thiols in the presence of a greater quantity of phenols and evenwhen the thiols are present in very small or trace quantities. Theselective thiol reaction takes place rapidly and to such a degree thatthe organo thiols are reacted with epoxide'substantially quantitativelyin the presence of the phenol. Moreover, while the catalytic effect ofthe phenol preferably in caustic solution causes the alkali solublethiols to react immediately, even alkali insoluble mercaptans arecatalyzed to react so that intimately contacted liquid hydrocarboncontaining residual alkali insoluble mercaptan may be sweetened whencontacted with the alkali phenolic solution for a period sufficient toprovide such intimate contact. The reaction product of the thiol and theepoxide such as alkylene oxide'is a valuable product soluble in'liquidhydrocarbon and exerts a substantial stabilizing effect upon crackedgasolines as an anti-oxidant.

Accordingly, in one useful application of this reaction, impure phenolmixtures such as are commercially available, as by extraction byhydrocarbon oils containing thiols, such as thiocresol, andlower-aliphatic mercaptan, may be purified to remove such sulfurcompounds substantially quantitatively by reaction with an epoxide,typically alkylene oxide, preferably ethylene oxide or propylene oxide.The reaction apparently is so strongly catalyzed by the phenol and goesso nearly to completion that little more than stoichiometric quantitiesof epoxide with respect to thiol need be used. However, since thereaction product is soluble in hydrocarbon, a solution of epoxide inliquid hydrocarbon in any concentration may be used to purify the phenolsolution.

Such reactionis outstandingly useful man-improved sweetening process forsour hydrocarbon oils such as gasoline, and for this purpose'only minutequantities of epoxide would be normally used. "Thus spent causticobtained by alkali washing of sour gasoline to form a spent causticsolution containing alkali phenolate and thiolate may be reacted withapartially sweetened liquid hydrocarbon to whichhasbeen added. suflicientepoxide such as ethylene oxide to react substantially quantitativelywith any residual mercaptan therein as well as with some of themercaptide in the spent caustic solution. One effect of such reaction isto catalyze the reaction of all the alkali insoluble mercaptan in theliquid hydrocarbon to an epoxide derivative thereof and also form;more

epoxide derivative of some of the mercaptide present in the spentcaustic. This treatment further forms a solution of the epoxide-thiolderivative in small quantity in the gasoline to stabilize the same. durethe gasoline is stabilized, and completely sweetened, using only minutequantities of epoxide therefor. The

reaction by catalysis of the alkali phenol solution is so highlyeflicient that the sweetening and stabilizing is relatively inexpensiveand far more economical than any heretofore proposed use of epoxide ingasoline sweetening.

Moreover, the ultimate removal of contaminating thiols from the alkaliphenolate solution by continued contact with epoxide solution in liquidhydrocarbon regenerates the same, so that phenols, a valuable commercialproduct, 1

may. now be recovered by neutralization of the alkali with acid asphenol relatively free of contaminating thiol compounds. However, suchthiol free alkali phenolate regenerated in this procedure may also beused if desired in extracting further quantities of alkali solublethiols from raw sour liquid hydrocarbon.

In the prior art it was suggested that higher epoxides in the presenceof oil soluble catalyst react with free hydrogen sulfide and inhibitshydrogen sulfide odor in lubricating oils containing sulfurizedadditives (Baker 2,684,943). It was further suggested that as little as0.05 weight percent of ethylene oxide in gasoline could 'be added to analkali washed sour gasoline to effect R may be hydrogen or any organic,preferably hydrocarbon radical, aliphatic, cyclo aliphatic, or aromaticcar bocyclic, but for purposes of sweetening sour liquid hydrocarbon itis preferred to use lower alkylene oxides wherein R is a 1 or 2 carbonatom alkyl, or hydrogen, because these are more easily handled, andreact more rapidly and efficiently. Useful higher epoxides usually forpurposes other than sweetening include amylene oxide, cyclohexene oxide,styrene oxide, epichlorohydrin, glycide, and decene oxide.

According to the present procedure using spent caustic containingextracted acid oils as catalyst for sweetening, it is found thatfar lessthan the minimum proposed in the art of 0.05 weight percent of ethyleneoxide may be used for far more effective sweetening. In fact as littleas 0.001 weight percent by the present procedure, and

I preferably from 0.001 to 0.04 weight percent of alkylene metho ds. Inpractical application, the alkylene oxidewill Patented July 19, 1960 IThus by that procehandling and the characteristics of the materials.

be used in slightly above, up to 150%, of the stoichiometric mercaptancontent of the sour gasoline whereby a quantity greatly less than theminimum considered possible in the art will eflfect the far more highlyeflicient sweetening.

Thus, applicants process applied to the sweetening of liquidhydrocarbons preferably comprises removing lower alkali soluble acidcomponents from sour gasoline by a caustic soda wash to produce a spentcaustic containing substantial quantities, at least and up to 60 volumepercent, of acid oils comprising alkali phenolate, mostly sodiumcresylate, alkalimercaptides such as sodium thiocresylate, lower alkalisoluble aliphatic mer captides and some other acidic impurities such asnaphthenic acids, as their alkali salts. The spent caustic will usuallycontain between and 50 volume percent of such acid oils. In sweetening,a sour liquid hydrocarbon such as gasoline stock is first washed withcaustic soda solution water to remove the alkali soluble acid oils. Apartially sweetened gasolineby alkaliwash then has added thereto aminute quantity of alkylene oxide, usually ethylene or propylene oxide,in quantity less thanabout 0.05 weight percent, and as a practicalmatter, the quantity of alkylene oxide added is preferably adjusted onthe basis of the residual alkali insoluble mercaptan content -of the 1partially sweetened liquid hydrocarbon, and this some of the thiolcontent of the spent caustic. It will be understood that any alkyleneoxide 'content within this range would operate to radically reduce themercaptan content to substantial nullity under the strong catalysis ofthe spent caustic rich in alkali phenolates, and the quantity ofalkylene oxide accordinglyneed only slightly exceed that needed forstoichiometric reaction with residual mercaptan.

The time, temperature and pressure and flow rates for reaction will beregulated primarily by economy in Thus the temperature used is dictatedlargely by the boiling point range of the liquid hydrocarbon to besweetened. The higher temperature is used for hydrocarbon liquids ofhigher end point, which might contain less readily reactable and heavierresidual mercaptan. For example,

the broadest range of reaction temperatures for sweetening a liquidhydrocarbon will generally be from about 50 to 200 F., but the thetemperature is preferably held to a narrower range depending upon theliquid hydrocarbon to be sweetened. For liquified gases and naturalgasolines a useful temperature of sweetening treatment is between 50 and85 F.; for wide BP range gasolines 75 to 120 F.; for naphthas 85 to 135F.; for kerosene 95 to 140 F.; and for diesel and furnace oils 105 to150 F.

The alkali washed partially sweetened liquid hydrocarbon containing aproper quantity of alkylene oxide is mixed by agitation with the spentcaustic and held at the selected temperature for a period of 1 to 45minutes, usually about 3 to 30 minutes, the greater reaction time givingthe more complete reaction.

The reaction may take place at atmospheric pressure at a reasonablerate, but for purposes of readily handling liquids under pumping flowfor commercial operation and to slightly increase the time of reactionby improving the intimacy of the mixture of reagents, slightly raisedpressures are preferred in a sweetening system, such for example as 10to 100 lbs. p.s.i. gauge. At the upper portion of the temperature andpressure ranges given, the reaction period needed is less and usually 3to minutes will suffice for very efficient sweetening.

Preliminary caustic wash of the liquid hydrocarbon is with causticsolutions of 5 to 50%, preferably to 45%, by weight of sodium hydroxidein water. The hydrocarbon stream may be scrubbed with 5 to 135% by 4volume of this caustic wash, preferably 20 to 50% by volume. Forcontinuous flow, 100 barrels per hour of liquid hydrocarbon may bescrubbed with 5 to 135 barrels per hour of caustic solution, preferably25 to 100 barrels per hour.

To illustrate the practical operation of this process for sweetening ofgasoline, reference is made to the attached diagrammatic flow sheet.Hydrocarbon fluid such as sour gasoline containing mercaptans, phenols,etc., enters the system through line 10 impelled by pump 12 which maybuild up pressure to whatever the system is operating at such as 10 to100 psi, and passed to a batch extractor 14 by way of line 16. Causticsoda, such as 50 B. or even higher sodium hydroxide solution in water,is made up in a supply tank 18 and passed to a dilution tank 20 by wayof line 22 where it is diluted to desired concentration of 5 to 50weight percent usually 20 to 45 weight percent, and thence pumpedthrough line 24 by pump26 into the batch extractor or scrubber 14. Thescrubbed gasoline leaves the extractor 14 through line 28 usuallypassing to storage. This alkali washed gasoline may boot a characterthat needs no further sweetening treatment, but if further sweetening isneeded it may be the starting material for further desulfurization. Forexample, a fluid catalytically cracked naphtha boiling in a range of 340to 460 F. containing'0.004 weight percent of mercaptans, mostlythiocresols, and. 0.25 weight percent of phenols, mostly cresols,scrubbed with a 50% caustic solution is usually sufficiently sweetenedfor use without further treatment with ethylene oxide. The causticsolution is recycled from line 30 by pump 32 and lines 34 and 36 throughthe batch extractor with succeeding batches of gasoline until the acidoil content ,a regenerative type extractor.

:has been built up in the caustic solution to more. than about 5volumepercent and usually 10 to 50 volume percent. The causticsolutionmay also be circulated in contact with other sour hydrocarbonbefore it is spent. Thereafter, the spent caustic is sent to used alkalisolution storage 38 by way of line 30, pump 32, and line 40.

For sweetening with ethylene oxide for example, according to the presentsweetening method, raw hydrocarbon containing mercaptan in quantity andcharacter which is not satisfactorily sweetened by simple caustic wash,such as wide range cracked gasoline or other hydrocarbon liquid asmentioned above, is drawn into the system by pump 46 through lines 42and 44 and sent to batch extractor 48. That batch extractor 48 allowsthe gasoline to be scrubbed by caustic solution also supplied fromtank'20 by way of pumps 26 and -'32, lines 24, 34 and 36, and as shownthe caustic may be the same solution that is circulated through batchextractor =14 recycling through lines 50 and 36 taking some flowfromline 34-and-impelled by pump 32.

The alkali washed gasoline before further treatment may be again washedwith caustic to further reduce the sulfur content, but since practicallyall of the alkali extractible acid oils have already been substantiallywith- 68, wherein live steam is passed from line 70 to effect removal ofmercaptans therefrom by volatilizing them through vent 72 andregenerating the alkali. The regenerated alkali after passing throughheat exchanger 64 is further cooled'in cooler 74 and recycled by pump 58to line 60 forre-use. The spent caustic after a time maybe-withdrawnfrom the system through line 76 of ethylene oxide is formed in gasoline.

amnesia '5 for disposal through line 78. i The twice alkali'scrubbedgasoline after leaving the regenerative extractor through line 80 ispassed to a settler 82 to remove any entrained alkali which is withdrawnthrough outlet 84. Alkali free gasoline is then passed for furthersweetening treatment in the system to line 86.

The regenerative extractor scrubbing may be dispensed with and only asingle wash performed in 48 may be applied to the gasoline in whichevent the regenerative extractor will be bypassed from batch extractor48 passing through line 88 and thence to line 86 for further treatment.

The further sweetening treatment of gasoline passing through line 86usually consists of first adding the controlled quantity of ethyleneoxide, less than about 0.05% preferably in only slight excess of theresidual mercaptan content in the gasoline passing through line 86. Forthis purpose, ethylene oxide is supplied from a drum 90 to a dilutiontank 92 wherein a concentrated solution That stock solution is used formore ready distribution, admixture with the gasoline to be sweetened,and for mos-t accurate control of the quantity of ethylene oxidesupplied. For the latter purpose-the solution of ethylene oxide isdistributed from a rate tank 94. For preparing the alkylene oxide supplysystem for use, inert gas such as methane or nitrogen is first passedinto the dilution and rate tanks from any suitable source by way oflines 95, 96 and 98 to purge all air from the ethylene oxide system,expelling the same through vents 100, 102 and 104' to free these tanksand lines from air. Thereafter, the vents are closed and the systempressurized to the samepressure as the gasoline passing in line 86.Diluent hydrocarbon liquid is then passed into the dilution tank 92through line 106 to desired level. Thereafter inert gas is passed intoline 96 under pressure to expel ethylene oxide from drum 90 into thedilution tank 92 to desired concentration as a concentrated solution ofethylene oxide in hydrocarbon, to substantial but known concentration offrom 1 to 100 volume percent, usually to 40 volume percent.Thereafterpthe concentrated ethylene oxide solution in hydrocarbon isexpelled by inert gas passed through line 108 from the dilution tank byWay of line 98 into the rate tank. The concentrated stock solution ofethylene oxide in hydrocarbon liquid under pressure of inert gas in line108 is then pumped by way of line 11-0 and pump 112 through valve 114which passes the solution at a cont-rolled rate and accurately controlsthe quantity admixed'with the gasoline passing in line 86.

This method of adding the ethylene oxide tothe gasoline to be sweetenedby first forming a stock solution makes the volumetric measurement ofthe solution of known ethylene oxide content to the gasoline to besweetened more accurate. Moreover, it allows the ethylene oxide to bepumped as a liquid and further reduces the danger of ethylene oxide frompolymerizing with itself as it often tends to do when handled in highconcentration.

The sour gasoline containing ethylene oxide is now contacted with spentcaustic solution containing acid oils. It may be passed through line11-6 to a scrubber 120 by way of line 118 and scrubbed with the spentalkali containing acid oils passed countercurrently through the scrubbertower 120. The spent caustic is obtained from line 40 sent to thescrubber by way of line 122, the used alkali solution being circulatedcountercurrently recycling with pump r123 by way of line 124 to the topof the scrubbing tower from the bottom until the mercaptan content ofthe spent alkali solution is exhausted. The mercaptan-free caustic isthen sent to a phenol recovery system through lines 126,156,168 and174-, or alternatively recycled from line 60a which connects with 30(not shown) for further use as a caustic wash liquid. The simplescrubbing of the gasoline containing ethylene oxide with used alkalisolution containing phenol in scrubber markedly reduces the meroaptancontent to a usefully sweet gasoline and that gasoline may be withdrawnfrom the top of the scrubber tower 120 through line 128 and from thesystem as treated hydrocarbon for any further treatment that may bedesired through line 130 by way of line 132.

However, far more efiicient rnercaptan removal is possible by passingthe sour gasoline containing ethylene oxide in line 116 to a reactionmixer 134 together with used alkali solution which will be pumped bypump 138 from the used alkali storage tank 38 by way of lines 136 and140, joining the gasoline containing ethylene oxide in line 116 as itenters the mixers 134. Thus the three'materials, sour gasoline, ethyleneoxide, and spent caustic solution containing at least 5 and up to 60volume percent of acidoils extracted from sour gasoline are intimatelyagitated or brought in intimate contact in the mixers for a period of lto 45 minutes and held at a temperature during this period as givenabove,

only phenols and other oxygenated compounds such as naphthenic acids maybe pumped by pump 133 to phenol recovery line 126 by way of lines 148,156, 168 and 174, or the mercaptan-free spent caustic containing phenolmay be'withdrawn from line 1% through lineand recycled for furthercaustic wash of sour gaso-- :line (not shown) to line 30. If desired thesweetened gasoline in line 128 may be again contacted with spent causticfrom line 140, both being passed into mixers 134.

Surprisingly great advantages are present by usingspent caustic solutionas a catalyst for improved sweeten-- ing of the sour gasoline. Forinstance, simple washing of sour cracked gasoline with about 20% causticsoda can reduce the mercaptan content by about 80% and higher causticcontent with repeated Washing can some-- times remove up to 90% but notmore, and most gasolines are inadequately sweetened thereby. Moreover,even simple contact of sour gasolines with ethylene oxide and alkali assuggested in the art gives inadequate sweet ening unless largequantities of ethylene oxide are used. For example, a gasoline having acontent of 0.01 weight percent of mercaptan to which 0.05 weight percentof ethylene oxide is added and contacted for 10 minutes? with 20%caustic solution had its mercaptan sulfur re-- duced to 0.0025 weightpercent. To this same gasoline mixture spent caustic in the sameconcentration but containing 15 volume percent of acid oils was nowadded and shaken for 3 more minutes and the mercaptan sulfur was thenfound to be reduced to 0.00006 weight percent, thereby indicating thatthe spent caustic reduces the sulfur content to about 4 that resultingfrom ordinary caustic treatment with the same minimum quantity ofethylene oxide contacted for a period of only 3 minutes. It is apparentthat in the presence of this highly activating phenolic spent causticsolution the quantity of alkylene oxide needed to reduce the mercaptaneven to a far greater degree, may be greatly reduced below the minimumquantity of alkylene oxide considered to be useful in the art.

The following table illustrates the effects of the present spot testsunder laboratory conditions. I a

co neshighly economical.

TABLE I Test 7 Copper No. Treatment No. of

Product 1 Washed twice with 10 vol. percent, 16 wt. percent, 5

caustic at 80 F.

2 Washed with 10 vol. percent, 30 wt. percent, caustic 4 3 Washed with10 vol. percent, 30 wt. percent, caustic 1.5 containing 24 vol. percentAlkyl Phenols and Thiophenols (Phenols and Thiophenolscxtracted from aoatelytically cracked naphtha boiling between 340- 450" F.) at 80 F.

4 Washed with 10 vol. percent, 30 wt. percent, caustic+ 3. 5

0.032 percent Ethylene Oxide at 80 I 4a Washed with 10 vol. percent 30m. percent caustic-l- 1.3

0.32 percent Ethylene Oxide at 80 F.

5 Washed with 10 vol. percent, 30 wt. percent caustic containing 24 vol.percent Alkyl Phenols and Thiophenols+0.32 percent Ethylene Oxide at 80F.

6 Washed with 10 vol. percent, 30 wt. percent caustic 0.75 containing 24percent Alkyl Phenols and Thinphcnols+0032 percent Ethylene Oxide at 80F.

7 Washed with 10 vol. percent, 30 wt. percent, caustic 0.65 containing24 vol. percent Alkyl Phenols and Tidephcnols+0.064 percent EthyleneOxide at 80 F.

8 Washed with 10 vol. percent, 30 Wt. percent, caustic 0.50 containing24 vol. percent Alkyl Phenols and Thinphenols+0.096 percent EthyleneOxide at 80 F. r

9 Washed with 10 vol. percent, 30 wt. percent, caustic 0.23 containing24 vol. percent Alkyl Phenols and Thiophenols+0.16 percent EthyleneOxide at 80 F.

10 First washed with caustic as in #2, then washed with 0.60

10 vol. percent 30 wt. percent caustic containing 24% Alkyl Phenol andThiophcnol+0.008 wt. percent Ethylene Oxide at 80 F. 11 Same as#l0+0.016 wt. percent Ethylene Oxide 0.20 12 Same as #i0+0.032 wt.percent Ethylene Oxide 0 The data shows that washing with ordinarycaustic at 80 F. reduces a 19 Copper No. gasoline to about with twocaustic washes and to 4 with a singlewashing of more concentratedcaustic. The presence of alkyl phenols and thiophenols in a 30 percentcaustic wash in test No. 3 still further reduced that Copper No. to 1.5,even in the absence of ethylene oxide. The Copper No. 3.5 obtainedin-test No. 4 does not reflect substantial reduction by ethylene oxideby using 032% in the presence of ordinary caustic; compare test No. 2with test No. 4. A much larger quantity (32%) of ethylene oxide, in thepresence of spent caustic containing acid oils reduced the Copper No. tozero in test No. 5. Tests 6 through 9 indicate that Copper Nos. below 1are also possible when using greatly reduced quantities of ethyleneoxide ranging from to 1 the quantity of ethylene oxide used in test No.5. For instance, further comparing test No. 4 with test No. 6, whereinthe same quantity of ethylene oxide was used, the presence of alkylphenols caused notably greater reduction of Copper No. from 3.5 to 0.75.Test No. 4a illustrates that much larger quantities of ethylene oxide doimprove the sweetening over test No. 4, but do not approach the resultsavailable in No. 5 wherein the same quantity ofethylene ox ide is usedin the preesnce of a phenolic catalyst. 'As illustrated in tests 6through 9 While the sulfur content in each case is very low, there issome variation thereof with the concentration of ethylene oxide in theseshort spot Washing tests. In contrast, tests 10, 11 and 12 using thesame respective quantities of ethylene oxide gives steadily improvedresults when the gasoline is first washed with ordinary caustic in apreliminary wash.

It will be apparent in practical figures of economy that the presentprocess using spent caustic to catalyze the reaction allows sweeteningof gasoline at a cost which is a mere fraction of that needed by knownsweetening methods using alkylene oxide. By the present procedure itbecomes possible to use extremely minute quantities, substantially lessthan the minimum regarded as necessary by the prior art, such as 0.05wt. percent of ethylene oxide. The present method therefore allowingsuch decreased necessary use of ethylene oxide be- 8 For example, toillustrate this point, the Arundalc process referred to above as priorart preferably uses from 0.2 to 0.8 weight percent of ethylene oxide,whereas, in contrast the present process may use less than the ,minimumquantity considered by Arundale to possibly opcrate. Thus referring to'Arundales table, operation Nos. 12, 24 and 56, it required from 0.4 to0.6 weight percent of ethylene oxide to reduce a 20 Copper No. gasolineto a Copper No. of 1. That quantity assuming 0.5 weight percent ofethylene oxide would cost 49 cents per barrel for sweetening. Incontrast merely on an experimental basis comparable to that shown byArundale,-it would cost 3.0 cents per barrel using phenolic spentcaustic as a catalyst, the quantity of ethylene oxide being 0.032 weightpercent as shown in test No. 6 above.

Of course, larger quantities of ethylene oxide will operate to reducemercaptan in applicants method using spent phenolic caustic to catalyzethe sweetening with some but lesser loss of economy than by otherprocedures because the reaction will run faster at lower temperaturesand with more efficient sweetening than available by such prior artmethods. Various manipulative procedures for contacting sour gasolinewith alkylene oxide and spent caustic may be applied. It is desirablefor purposes of economy that the sour gasoline be first washed withcaustic to remove alkali soluble phenol and mercaptan, because thisreduces the quantity of residual mercaptan in the liquid hydrocarbon tobe sweetened and thereby reduces the quantity of alkyleneoxidenccessarily required. Consequently, in actual plant operation onthermally cracked gasoline, the commercial cost will reduce to 2.0 centsper barrel to obtain a Copper No. of less than 1.0.

This point is illustrated by reference to test No. 6 in applicants tableabove. For instance, in a spot laboratory test using 0.032 weightpercent ethylene oxide without preliminary caustic wash, a Copper No. of0.75 was obtained (0.001 Weight percent of mcrcaptan sulfur). If thesame gasoline is first given a preliminary caustic wash according toapplicants preferred procedure the original mercaptan content of thegasoline, 0.026 weight percent is reduced by the preliminary wash to0.010 weight percent of residual mercaptan sulfur in the gasoline. Thiswould require only 0.013 weight percent of ethylene oxide to reduce themercaptan sulfur content to the same 0.75 Copper No. (0.001 weightpercent), thus indicating that the necessary quantity of alkylene oxidemay be reduced to about /3 of that necessary where a preliminary causticwash is applied.

Moreover, that preliminary caustic wash while removing alkali solubleacid oils serves to make available the spent caustic used to catalyzethe alkylene oxide sweetening. However, that preliminary caustic washmay be omitted, with sacrifice of some substantial economy inherent inthe method, if desired.

The alkylene oxide preferentially reacts with the mercaptans, bothalkali soluble aliphatic mercaptans and thiophenols, in the spentcaustic, the phenols and alkyl phenols serving to catalyze thatreaction. In the presence of the phenolic concentrate contained in thespent caustic, the alkylene oxide also reacts with higher causticinsoluble mercaptans in the alkali washed gasoline. The

. mercapto-cpoxide reactio'n product is soluble in the by- '9 widervariation of products by mercapto-epoxide reaction, various otherepoxides such as higher epoxides listed above may be used for reactionwith the mercaptan in spent caustic to regenerate the caustic, or toform gasoline stabilizers, or in gasoline in the sweetening andstabilization thereo'f.

Example I A fluid catalytically cracked naphtha boiling in the range of340 to 460 F. containing 0.004 weight percent of mercaptans mostlythiocresols and 0.25 weight percent of phenolic compounds mostly cresolswas introduced into batch scrubber 14 at a flow rate of 100 barrels perhour. It was scrubbed with a 38 weight percent solution of caustic sodaintroduced into the scrubber at a rate of 75 barrels per hour, thecaustic solution being recycled until the caustic had absorbed 20 volumepercent of acid oils and it was then sent to used alkali storage 33 byway of line 40 and replaced with a fresh batch of alkali. The causticwashed cracked gasoline was not further sweetened.

A wide boiling range thermally cracked raw sour gasoline was introducedto batch extractor 48 and washed by circulation of the same caustic sodasolution and at the same rate simultaneously with washing of gasoline inbatch 14. That raw gasoline initially contained 0.016 Weight percent ofmercaptan and consisted of a wide range cycle oil from a catalyticcracking unit containing coker distillate and has a boiling point in therange of 80 to 435 mercaptan content had been reduced to 0.010 weightpercent. The caustic washed distillate was then sent directly from batchextractor 48, by way of lines 88 and 116 and after having added thereto0.03 weight percent of, ethylene oxide introduced in accurate quantitiesby way of valve 114 was pumped by way of line 118 to the top of thescrubbing tower 120. The system had been pressurized to 50 lbs. p.s.i.and the distillate was maintained at a temperature of 95 F. It wasWashed at the same flow rate of 100 barrels per hour countercurrently inscrubber t'ower 120 with 75 barrels per ho'ur of the 38 weight 'percentspent caustic containing-20 volume percent of'acid oil, also heated to95 F., from used alkalistorage 38 by way of line 122. The mercap tancontent of the gasoline leaving the tower in line 128 had been reducedto 0.002 weight percent. The gasoline was then passed to mixers 134 incontact with 75 volume percent of the same used caustic solution butagitated for minutes in mixer 134 and finally passed to the hydrocarbonsettling chamber 144;and then out through line 130 as sweetenedgasoline. It now contained 0.0006 weight percent of mercaptan therebyindicating that by increasing the time of contact of caustic and acidoil with the gasoline, the mercaptan removal is-greater.

Example II The same wide boiling range thermally-cracked-gaso line ofExample I was divided-into separate flow portions, each being introducedto lines 10 and 42 respectively so that batch extractors '14and'48 wereoperated upon the same raw gasoline and both initially extractedproducts were. recombined-by way'of line152' and line 52 and sent to aregenerative extractor '54 which contained fresh 38% caustic. 'Thatregenerative extractor had the caustic continuously recycled fromextractor 54 through regenerator 68 and the spent caustic was ultimatelydisposed of through line 78 outside of the system. After settling insettler 82 the doubly extracted raw gasoline stock which then contained0.01 weight percent of mercaptan was passed through line 86 and had0.035 weight percent of ethylene oxide dissolved in hydrocarbon solventaccurately added thereto through valve 114. The ethylene oxidecontaining gasoline was then passed to the mixer 134 through line 116together with 75 volume percent of 38 weight percent spent causticsolution containing 20% of acid oil and agitated in the mixers 134 for aF. After leaving batch extractor 48 the Example III The sweetening asdescribed in Example I was performed upon a fluid catalytically crackedlight gasoline boiling between '370 F. It contained initially 0.03weight percent of phenols and 0.003 weight percent of mercaptans. Afterinitial 20% alkali wash it had added thereto 0.005 weight percent ofethylene oxide and was scrubbed in scrubber in contact with a 20 weightpercent spent caustic solution containing 12 volume percent of acidoils. It was found that the mercaptan content had been reduced to 0.0002weight percent at a cost of 0.48 cents per barrel.

It will be noted that in general the higher the percent of caustic andacid oil in the spent caustic solution the better the conversion ofmercaptans. The greater the contact time, the better the removal.Temperature has no substantial eifect except that it is generallypreferred to use somewhat raised temperatures because of the consequentreductionofviscosity of the caustic solution al lowing greaterquantities -to' be circulated 'and thereby higher spent caustic togasoline ratios which gives more eflicicnt sweetening. The higher theethylene oxide concentration, the more rapid and, complete removaletfected. These examples acco'rdingly indicate that very .efiicientsweetening of gasoline is possible using. far less quantity of ethyleneoxide than possible by prior art practices;

REGENERATION OF SPENT CAUSTIC -In the Examples'h'to llI given toillustrate-sweetening, substantial quantities of mercaptan are withdrawnby reaction of the slight excess of ethylene oxide in the hydrocarbonwith-the-mercaptan in the spent caustic, sufficient to 'allow themercaptan content of the spent caustic to be continuously reduced to theend that the caustic maybe recirculated for further use-as a causticwash in preliminary washing as in batch extractors 14, 48 or 54. It ispossible, however, using the present selective reaction of alkyleneoxide on mercaptan in the presence of phenolic acid oil to completelyremove the contaminating mercaptan, thereby allowing recovery of boththe product of the reaction of alkylene oxide with mercaptan and'thepurified phenolic oil which is illustrated in the following examples.

Example IV A spent'caustic solution containing 40% of caustic soda inwater and 52 volume percent of acid oils consisting of a crude mixtureof approximately 92% alkyl phenols and phenols, mostly cresols, about 2%of carboxylic acids of the character of naphthenic acid, and about 6% ofmercaptans ,of whichabout 154% are lower alkali soluble aliphaticinercaptans and about 412% are thioph'e'nols, ino'stly' thiocresols, ispassed from spent alkali solution tank 38 to a mixer 154 by way of lines156, 149 and 148, pump 138 and line 136. It is contacted with ahydrocarbon solvent which may be a relatively pure hydrocarbon such assynthetic isooctane introduced into settling tank 158 through line 160and drawn from that settling tank 158 through line 162 by pump 164,which passes the hydrocarbon in intimate contact with the spent causticflowing from line 156, both into the mixer 154. Pump 166 passes ethyleneoxide into the hydrocarbon line 162 to form a solution thereininsubstantial quantity to form a concentrate which Will correspond tothe strength of the ethylene oxidemercaptan reaction product to bedissolved in the hydrocarbon as a concentrate. About 10 weight percentof ethylene oxide with respect to the hydrocarbon in tank 158 isintroduced by pump 166 together with hydrocarbon from line 162 andcaustic from line 148 into mixer 154 by way of line 156. Reaction takesplace at ambient temperature and the mixture passes back to thehydrocarbon tank 158 through line 166, wherein the caustic solution, nowfree of mercaptan, isallowed to settle. The purified caustic iswithdrawn as a lower liquid layer through line 168 and pump 170 by whichit is either recycled from line 174 to the system as a caustic washsolution through line 30a or to a phenol recovery tank 176. Thehydrocarbon in tank 158, which contains an excess of ethylene oxide, isrecycled through line 162 and pump 164 to the mixer to react with morespent caustic until it is completely reacted and the concentratedhydrocarbon solution in tank 160 is withdrawn through line 172 forfurther purification of epoxide-mercaptan reaction product in anothersystem. Such system (not shown) may consist of a rectifier which willremove the hydrocarbon and fractionate the product into select fractionsof narrow boiling point range. The purified alkali phenolic solutionsent to acid reaction tank 176 has a stoichiomctric quantity ofneutralizing acid, typically sulfuric acid, added thereto through line178. The acid phenol solution is withdrawn through line 180 and sent toa rectifier from which phenolic oils are separated by distillationremoving first the water and then distilling the phenols into selectfractions.

Example,

with ethylene oxide dissolved in petroleum ether by scrubbing in a batchscrubber, allowing the hydrocarbon and aqueous layers to separate bysettling, withdrawing the aqueous alkaline phenol layer and finallyneutralizing with dilute sulfuric B.) acid. A phenol solution originallycontaining 0.52% sulfur compounds has the sulfur content reduced to0.00002% sulfur when washed with petroleum ether containing 1.0% byweight of ethylene oxide for 40 minutes.

Example VI The solutions were then allowed to settle and separate.

The aqueous caustic layer'was neutralized with 50% sulfuric acid. Theneutral aqueous solution was then distilled. The mercaptan content ofthe phenols was 0% The total sulfur content was 0.04 weight percent.

Example VII Thermally cracked gasoline of Example II has added thereto asufficient quantity of a 10% concentrate of ethylene oxide-mercaptanreaction product in gasoline as formed in Example IV, for forming a 0.5weight percent of the reaction product in the cracked gasoline. That 12Example VIII Much smaller quantities of dissolved ethyleneoxidemercaptan reaction product resulting from ordinary sweeteningwithout specific increase of quantity, however, exerts an enhancedstabilizing effect upon ordinary phenolic type inhibitors that may beconventionally added to gasoline for stabilizing the same against gumformation resulting from oxidation of the gasoline in storage. Toillustrate this a thermally cracked gasoline is first washed with a 45weight percent spent caustic soda solution containing 20 volume percentof acid oils. It has a 100 lb. p.s.i. oxygen induction period at 212 F.of minutes and a copper dish gum content of 7 mg. per 100 ml. Incontrast, that same gasoline to which 0.05 weight percent of ethyleneoxide was added and then washed with the same caustic wash was found tohave an induction period of 100 minutes and a copper dish gum of 35 mg.per 100 ml. Thereafter controlled quantities of a standard gum inhibitorwas added to each sample of gasoline, the gum inhibitor being ditertiarybutyl-paracresol. The following table shows the effect of bothtreatments with variable quantities of gum inhibitor.

To illustrate isolation of the ethylene oxide-mercapto reaction productuseful as a gum inhibitor, a 30 wt. percent caustic solution containing10% by volume phenols, 3% by wt. mercaptans, and 0.1% by wt. sulfideswas contacted with a mixture of 50% commercial benzol and 50% petroleumether (90-160 F.) containing ethylene oxide. Two thousand ml. of thehydrocarbon containing 0.05 wt. percent ethylene oxide was contactedwith 15 grams of the caustic for three minutes. The ethylene oxideconcentration was maintained at 0.05 wt. percent and the processrepeated until a total of 200 grams of caustic was treated. Analysis ofthe causticrevealed-0% sulfide and 0% mercaptan. The hydrocarbon mixturewas evaporated on a steam bath. The oil residue weighed 9.8 grams. Thismaterial was free of mercaptans and a qualitative analysis revealed analcoholic functional group and sulfur thus- RS-CH -CH OH.

cracked gasoline, obtained from extractor 14 after caustic wash toremove phenols and sulfur, is unstable and has an induction period in abomb at 212 F. under 100 lbs. oxygen pressure of 100 minutes. Afteraddition of the reaction product solution, it was found to have aninduction period of 2% hours, thereby indicating that the reactionproduct is an efiicient stabilizer and anti-oxidant for the readilyoxidizable gasoline. I

Example A concentrate of ethylene oxide-mercaptan reaction product ingasoline as produced in Example IV was dis tilled to remove thehydrocarbon and fractionated to separate a fraction boiling at 530 F.ilt was found to be substantially pure monoethanol meta tolyl sulfidehaving the following structure:

S-CHzCHzOH It was added to the same catalytically cracked gasoline inquantity of 0.1 weight percent as in Example VI and found toimpart aninduction period thereto of 4% hours.

It will be appreciated that the present invention has many applicationsflowing from the fact that phenols selectively catalyzed the reaction ofepoxides with mercaptan. Thus many gasoline sweetening procedures may beused with this catalysis to allow sweetening with great economy. Crudephenols themselves are readily purified of mercaptan content byselective reaction with epoxide. Spent caustic solutions containing acidoils contaminated with mercaptan are readily regenerated to remove themercaptan. That spent caustic most efliciently contains at least about 5vol. percent of phenols, but lesser quantities such as 1% provide some,but less efi'icient catalysis. Similarly the phenol in acid formprovides substantial catalytic activity, but are most effective insubstantially alkaline solution containing at least 5% alkali. Thereaction may be applied to form various epoxy-mercapto derivatives usingmercaptan other than available by extraction from petroleum.

Accordingly, it is intended that the examples and illustrations of. flowarrangement for handling of gasoline in the sweetening thereof andregeneration of spent caustic solutions be regarded as illustrative andnot limiting except as defined in the claims appended hereto.

This application is a division of my co-pending application Serial No.565,289, filed December 21, 1955 now Patent No. 2,862,804.

I claim:

1. The process of regenerating spent aqueous causu'c soda solutioncontaining alkali metal phenolates and alkali metal mercaptides, thequantity of alkali phenolates being at least 5% by weight, comprisingdissolving an organic epoxide in a liquid hydrocarbon solvent andselectively reacting by intimately contacting the solvent solution ofepoxide with the said spent caustic solution to form a substantiallyaqueous mercaptan-free solution of caustic soda and phenolic oils and awater immiscible V A solvent solution of epoxide-mercaptan reactionproduct and separating the solutions. I

2. The process of regenerating spent aqueous caustic I soda solutionused in the refining of mercaptan containsaid process comprisingextracting the mercaptide by selective reaction of said spent causticsoda solution with organic epoxide dissolved in a hydrocarbon solvent bycontacting the said spent caustic and hydrocarbon A epoxide solutions,separatingthe mercaptan-free alkali phenolate solution from the solutionof epoxide-mercaptan reaction product dissolved in the hydrocarbonsolvent and acidifying the caustic solution to recover the phenols.

3. The process of regenerating spent aqueous caustic soda solutioncontaining acid oils comprising alkali phenolates in quantity of atleast 5% by weight and mercaptides said process comprising extractingthe mercaptide by selective reaction thereof with organic epoxidedissolved in a hydrocarbon solvent by contacting the said spent causticand hydrocarbon epoxide solution, separating the hydrocarbon solution ofepoxide-meroaptan reaction product and purifying the same by fractionaldistillation.

4. The process of regenerating spent aqueous caustic soda solution asdefined in claim 1 wherein the epoxide is a lower aliphatic epoxide.

References Cited in the file of this patent UNITED STATES PATENTS2,530,561 Arnold etal. Nov. 21, 1950 2,771,404 Iezl et a1. Nov. 20, 19562,794,768 Brooks June 4, 1957

1. THE PROCESS OF REGENERATING SPENT AQUEOUS CAUSTIC SODA SOLUTIONCONTAINING ALKALI METAL PHENOLATES AND ALKALI METAL MERCAPTIDES, THEQUANTITY OF ALKALI PHENOLATES BEING AT LEAST 5% BY WEIGHT, COMPRISINGDISSOLVING AN ORGANIC EPOXIDE IN A LIQUID HYDROCARBON SOLVENT ANDSELECTIVELY REACTING BY INTIMATELY CONTACTING THE SOLVENT SOLUTION OFEPOXIDE WITH THE SPENT CAUSTIC SOLUTION TO FORM A SUBSTANTIALLY AQUEOUSMERCAPTAN-FREE SOLUTION OF CAUSTIC SODA AND PHENOLIC OILS AND A WATERIMMISCIBLE SOLVENT SOLUTION OF EPOXIDE-MERCAPTAN REACTION PRODUCT ANDSEPARATING THE SOLUTIONS.